Generally, the working theorem of an acoustic touch screen is forming a uniform acoustic field on a surface of the glass substrate, and controlling the emitting acoustic and receiving reflection acoustic of the X and Y directions respectively by a computing circuit of a control card. And then computing the vibration of the receiving reflection acoustic to secure the X and Y coordinates of a touch point.
However, there exists a certain loss (about 0.25 dB/CM) while the acoustic transmits over the surface of the glass substrate, therefore, when designing reflection stripes of an acoustic touch screen, for securing the uniform of the reflection acoustic, it must satisfy the following two conditions: (1) the distance between the reflection stripe must be an integral times to an acoustic wavelength λ to secure the resonance transmission between two adjacent reflection stripes; (2) for securing the uniform of the reflection acoustic, the distributing condition of the reflection stripe is the reflection stripe must be distributed from sparse to dense to the point of incidence.
The prior art design method almost follows the preceding two conditions to secure the distributing of the reflection stripe elementary, and uses testing method to draw out, increase or decrease the reflection stripe by manpower to achieve a uniform acoustic field on the surface of the glass substrate. However, the acoustic field designed by prior art method while transmission on the surface of the glass substrate is limited by two preceding necessary conditions. During the reflection stripe distributing from sparse to dense to the point of incidence process, there exists a abruptly amplitude vibration of the reflection stripe at Nλ to (N-1)λ distance transition, therefore, the acoustic field designed by prior art method cannot satisfy the flat and the uniform request of the reflection acoustic.
Furthermore, European Patent No. 0,190,734 B1 issued to Adler et al. for ┌ACOUSTIC WAVE TOUCH PANEL SYSTEM┘ provides an acoustic wave touch panel system for recognizing and responding to touch along a predetermined coordinate axis on the touch screen (16), the system (10) including surface wave transducer means coupling input and output transducer means (T1, T2; R1, R2), respectively, coupled to the substrate surface (16) and input circuit means (25) associated with the input transducer means (T1, T2) for generating surface wave on the substrate surface (16) in a plurality of paths (Pv, Ph) between the input and output transducers (T1, T2; R1, R2) and output circuit means (23) coupled to the output transducer means (R1, R2) for detecting the position of a touch on the substrate (16) characterized in that the system including surface wave redirecting means (G1, G2, G3, G4) coupled to the substrate surface (16) for redirecting surface wave burst components derived from a burst of surface waves produced by the input transducer means (T1, T2) across the surface (16) to the output transducer means (R1, R2) along a plurality of paths (Pv, Ph) of different lengths which are respectively associated with different positions along the coordinate axis on the substrate surface (16), and the output circuit means (23) being capable of detecting touch-induced amplitude damping of received wave burst components by the fact of that a touch on the substrate surface (16).
Referring to FIG. 1, there shows the reflection stripe design on a touch screen (50) according to the European Patent No. 0,190,734 B1. As shown in FIG. 1, the input transducer means (T1, T2) and output transducer means (R1, R2) positioned respectively on the touch screen (50), wherein, the reflection stripes (51, 52, 53, and 54) are distributed from sparse to dense besides each transducer means (T1, T2; R1, R2) first, these reflection stripes (51, 52, 53, and 54) are assumed a basic shape of a reflection row as follow: the size of each reflection bars is equal and the distance between each reflection bars is equal and forms a 45 angle to the acoustic wave emitting source, etc.
The distance between two adjacent reflection bars is a wavelength of the emitting acoustic wave, such reflection bars row, making the energy dense of the acoustic wave exhaustion gradually, even disappear. As shown in FIG. 1, the acoustic field designed by prior art method follows the two preceding necessary conditions, during the reflection stripe distributing from sparse to dense to the point of incidence process, there exists a abruptly amplitude vibration of the reflection stripe at Nλ to (N-1)λ distance transition, therefore, the acoustic field designed by prior art method cannot satisfy the flat and the uniform request of the reflection acoustic.